1. Field of the Invention
This invention relates to an improvement to Exhaust Gas Recirculation (EGR) Systems and in particular to a metal screen affixed to a carbon gasket for sealing the EGR valve to the manifold of an automobile engine and providing an effective barrier to keep large exhaust carbon flakes from entering the EGR system and clogging the valve.
2. Description of the Prior Art
There are several prior art attempts to combine a gasket with a screen to filter fluid streams. For example, Powers U.S. Pat. No. 3,124,930 discloses a catalyst screen attached to a gasket which is placed between the exhaust manifold and engine block. The gases leaving the cylinders will, while very hot, be in contact with the catalyst member. The high temperatures available at this point remove a substantial percentage of the unburned hydrocarbons. Powers does not consider the screen as a blocking member since all of the exhaust must pass through, however, accumulation of carbon particles will eventually totally block the screen and render it useless. The strainer gasket for sanitary piping systems disclosed in Hirsch U.S. Pat. No. 3,421,631 discloses an in-line filter screen which is formed within the gasket. The filter screen shown by Hirsch also suffers from the same defect as Powers and would eventually be clogged with impurities. Crook U.S. Pat. No. 3,206,216 discusses the difficulties associated with combining a screen with a gasket in the prior art and solves the problems with a one-piece gasket/filter. Large flakes would also block the fluid stream and would have to be disassembled periodically.
One prior art attempt by a major automobile manufacturer to solve the problem of valve clogging was to change the structure of the valve. In a notice to service facilities, it was noted that for the 5.0L engine EGR system, two major improvements were made over previous systems. The first was a stainless steel EGR valve. This valve is constructed of stainless steel to reduce the possibility of clogging. The second improvement is the replacement of the EGR solenoids with an electronic vacuum regulator. Although the changes did reduce some of the carbon buildup on the valve itself, it did not solve the problem of carbon building up within the manifold, breaking off in large flakes, and clogging the valve. None of the prior art devices have solved the problem of eliminating large carbon flakes from the fluid stream and preventing blocking of the screening material.